Machine for cutting holes with annular cutters

Abstract

There is disclosed an air motor adapted to rotate and axially shift an arbor having an annular cutter attached thereto. Within the arbor a plunger is slideably arranged with its leading end bearing against a pointed pilot pin at the center of the cutter. The plunger is biased forwardly by either a spring cartridge or a piston-cylinder assembly so as to apply a predetermined constant or programmable pressure on the pilot pin throughout the entire cutting cycle. When the cutter penetrates through the under face of the workpiece, the pressure on the plunger is reduced to a very low value so that the slug within the cutter will be ejected at a relatively slow safe velocity.

I claim: 
     
       1. A machine for cutting holes in a workpiece comprising, a base, a motor, means for mounting said motor in a fixed position on said base, an axially shiftable, rotary driven spindle on said motor, an arbor fixedly connected at its rear end to said spindle to rotate and shift axially with the spindle, said arbor having means at its front end for mounting thereon an annular cutter having a coaxial pointed pilot pin shiftable axially therethrough, means on said base for supporting a workpiece thereon in a fixed position spaced axially forwardly beyond the leading end of the cutter when the spindle is in its retracted position, said spindle being adapted to be advanced axially to cause the leading end of the cutter to engage and cut a circular groove in the adjacent face of a workpiece supported on said base, said arbor having a central axial bore therein, a plunger slideable axially in said bore, means for operably connecting the forward end of the plunger to the rear end of the pilot pin, means for applying a predetermined maximum axial force to said plunger of sufficient magnitude to cause the front pointed end of the pilot pin to firmly engage said face of the workpiece in an axially fixed first position with said maximum force at the axial center of the hole to be formed therein, and means for reducing the force applied by the pilot pin to the workpiece to a value very substantially lower than the magnitude of said maximum force whenever the pointed end of the pilot pin has been displaced axially forwardly beyond said fixed position to a predetermined second fixed position only slightly beyond said face of the workpiece, whereby, as soon as the cutter penetrates through the workpiece and the plunger has displaced the pointed end of the pilot pin and the circular slug within the cutter to said second position, the force exerted by the pilot pin on said slug will have been reduced to said very low value. 
     
     
       2. A machine as called for in claim 1 wherein said force reducing means is adapted to reduce said maximum force to substantially zero when said pilot pin has been displaced to said second fixed position beyond said face of the workpiece. 
     
     
       3. A machine as called for in claim 2 wherein said force reducing means comprises means for limiting axial displacement of said plunger in an axially forward direction to a position wherein the forward end of the pilot pin is located at said second fixed position. 
     
     
       4. A machine as called for in claim 3 wherein said means for limiting axial movement of the plunger are adjustable to vary said second fixed position of the pilot pin. 
     
     
       5. A machine as called for in claim 1 wherein said means for applying said axial force to said plunger comprises a sleeve surrounding said arbor and axially slideable thereon, said plunger being connected to said sleeve for axial movement therewith and means for applying said force to said sleeve. 
     
     
       6. A machine as called for in claim 5 wherein said means for reducing said force comprises means fixed relative to said motor and adapted to be abutted by said sleeve when the sleeve is displaced forwardly to a predetermined position relative to said motor. 
     
     
       7. A machine as called for in claim 6 wherein said sleeve comprises a piston and including means fixed relative to the motor and defining a cylinder in which the piston is axially shiftable, said force applying means comprising means for applying pressure fluid to one side of the piston to displace the plunger and the pilot pin forwardly. 
     
     
       8. A machine as called for in claim 7 including means for applying fluid pressure to the opposite side of the piston to retract the plunger and pilot pin. 
     
     
       9. A machine as called for in claim 1 wherein said force applying means comprises a fluid cylinder fixed relative to said motor, a piston axially shiftable in said cylinder, means forming a driving connection between said piston and plunger and means for directing fluid under pressure to one side of the piston to displace the plunger in an axially forward direction. 
     
     
       10. A machine as called for in claim 9 including means for directing fluid under pressure to the opposite side of said piston for retracting the plunger and pilot pin. 
     
     
       11. A machine as called for in claim 9 including means for varying the pressure applied to said one side of said piston for adjusting said maximum force to a desired magnitude. 
     
     
       12. A machine as called for in claim 9 including means for varying the rate of flow of pressure fluid to said one side of said piston to control the rate of displacement of said plunger. 
     
     
       13. A machine as called for in claim 9 wherein said means for reducing said force comprises means for reducing the pressure of the fluid directed to said one side of said piston. 
     
     
       14. A machine as called for in claim 13 including means for actuating the means for reducing said pressure in response to displacement of the arbor in a forward direction. 
     
     
       15. A machine as called for in claim 14 wherein said actuating means are adapted to actuate the pressure reducing means before the pointed end of the pilot pin has been displaced to said second fixed position. 
     
     
       16. A machine as called for in claim 9 wherein said means for reducing said force comprises an abutment fixed relative to said fluid cylinder and adapted to be engaged by said piston to limit axial movement thereof in a forward direction. 
     
     
       17. A machine as called for in claim 1 wherein said means for interconnecting the forward end of the plunger with the rear end of the pilot pin includes an axially compressible member disposed between the pilot pin and plunger biasing the pilot pin axially forwardly, said member being axially compressible to a position wherein a substantially solid driving connection is established between the pilot pin and plunger by an axial force which is only a small fraction of said maximum force whereby, when the front end of the pilot pin engages a workpiece and said maximum force is applied to the plunger, a substantially solid driving connection is established between the plunger and the pilot pin. 
     
     
       18. A machine as called for in claim 17 wherein said compressible member comprises a light coil spring. 
     
     
       19. A machine as called for in claim 1 including means responsive to forward movement of said arbor to a predetermined position for applying said maximum force to the plunger before the leading end of the cutter engages said face of the workpiece. 
     
     
       20. A machine as called for in claim 1 wherein said force applying means is adapted to apply a force of constant magnitude to said plunger. 
     
     
       21. A machine as called for in claim 20 wherein said means for applying said substantially constant force to the plunger comprises compression spring means axially compressed between a first abutment fixed relative to the motor and a second abutment fixed relative to the plunger. 
     
     
       22. A machine as called for in claim 21 wherein said first abutment is axially adjustable relative to the motor for varying the value of said substantially constant force. 
     
     
       23. A machine as called for in claim 22 including releasable trigger means for initially compressing said spring means to a length less than the distance between said abutments to thereby apply an initial force to the plunger substantially greater than said constant force whereby, when said trigger means are released, the pointed front end of the pilot pin is impacted against and forms a centering indentation in said face of the workpiece. 
     
     
       24. A machine as called for in claim 21 including an axially shiftable sleeve on said arbor connected with said plunger for axial movement therewith, said second abutment being formed on said sleeve and engaging the forward end of said compression spring means. 
     
     
       25. A machine as called for in claim 24 wherein said first abutment comprises an annular member surrounding said arbor. 
     
     
       26. A machine as called for in claim 25 wherein said motor has an annular forward extension thereon, said first abutment being axially adjustable within said extension. 
     
     
       27. A machine as called for in claim 26 wherein said annular member has an axially threaded connection with said forward extension. 
     
     
       28. A machine as called for in claim 26 wherein said means for reducing said force comprises an abutment on said extension adapted to engage said sleeve and limit the forward movement thereof. 
     
     
       29. A machine as called for in claim 28 wherein said last-mentioned abutment is axially adjustable on said extension. 
     
     
       30. A machine as called for in claim 1 including means for retracting the plunger to a position wherein the pointed end of the pilot pin is disposed in a third fixed position spaced rearwardly from said face of the workpiece and for applying an axial forward force to said plunger substantially higher than said maximum force when the plunger is in said retracted position and means responsive to movement of the arbor to a predetermined forward position for causing said plunger to move forwardly under the bias of said higher force whereby to cause the pointed end of the pilot pin to be impacted against and form a centering indentation in said face of the workpiece and thereby assume said first position. 
     
     
       31. A machine as called for in claim 1 wherein said pilot pin has a close sliding fit in said cutter and including bearing means on said motor rotatably supporting said arbor adjacent the front end thereof. 
     
     
       32. A machine as called for in claim 31 wherein the connection between the front end of the spindle and the rear end of the arbor comprises a universal joint.